1. Technical Field
The present disclosure relates to a two-beam interference apparatus and a two-beam interference exposure system.
2. Related Art
The miniaturization and increased levels of integration of semiconductor integrated circuits have led to demands to increase the resolutions of semiconductor exposure apparatuses (hereinafter simply referred to as “exposure apparatuses”). Accordingly, advances are being made in the reduction of the wavelengths of light output from exposure light sources. Gas laser devices are being used as exposure light sources in place of conventional mercury lamps. At the present, a KrF excimer laser device that outputs ultraviolet light having a wavelength of 248 nm and an ArF excimer laser device that outputs ultraviolet light having a wavelength of 193 nm are used as gas laser devices for the exposure.
Immersion exposure, in which the apparent wavelength of an exposure light source is reduced by filling a gap between a projection lens of the exposure apparatus and a wafer with a liquid and changing the refractive index of the gap, is being researched as the next-generation exposure technique. In a case where the immersion exposure is carried out using the ArF excimer laser device as the exposure light source, the wafer is irradiated with the ultraviolet light having a wavelength of 134 nm within the liquid. This technique is called ArF immersion exposure, and this ArF immersion exposure is also sometimes referred to as the “ArF immersion lithography”.
Because the width of the natural oscillation of a KrF or ArF excimer laser device is approximately 350 pm to 400 pm and wide, chromatic aberration occurs when the projection lens in the device is used, which in turn causes the resolution to deteriorate. Accordingly, it is necessary to narrow the spectral line width of the laser beam output from the gas laser device until the chromatic aberration reaches a level that may be negligible. The spectral line width is also sometimes called the “spectral width”. For this reason, a line narrow module having a line narrowing element (etalon, grating, etc.) is provided within a laser resonator of the gas laser device, and the narrowing of spectral width is realized using this line narrow module. A laser device that narrows the spectral width in this manner is called a narrow-band laser device.
In addition, techniques have been developed, which carries out the circuit design of the devices using the line-and-space (L & S) as the fundamental patterns. For this reason, much attention are drawn to the two-beam interference apparatus that may be used as an apparatus to form the line-and-space patterns.
Related techniques may be found in U.S. Pat. Nos. 7,088,758, 7,154,928, 6,304,318, and 5,759,744, and Japanese Laid-Open Patent Publications No. 2002-329911, No. 2003-5233, and No. 2008-277618, for example.